THE SUFFOLK OTTER SURVEY
383
expected to hold otters. This would indicate that there was adequate habitat for three to five otter territories. Research between 1970 and 1972, although again not conclusive, tended to point to three territories with possibly a fourth. This roughly agrees with Erlinge's work and it would therefore be reasonable to assume that a density of one otter per 10 kms. of river was a good average for Suffolk, though the marshes may contain higher numbers. Listed below in TABLE 2 are the 12 categories given in the Results section. In brackets are given the number of otters thought at present to be in these areas. These figures have at least a 25 % tolerance. It is unfortunate that no previous figures are available which would allow for a comparison. It is therefore impossible to say if the present status of the otter is the Optimum or merely a vestigial population. Old hunt returns and other references for the period 1870 to 1940, seem to show that otters were being found on almost every river in the county. Ticehurst, 1932, appears to confirm this when he says, "There is hardly a suitable stream and certainly no Broad in the county that lacks otters". Probably the status quo was maintained until the late 1940s but from that date there appears to have been a steady downward trend in some areas. A number of factors have contributed to the otter's decline and chief among these must be counted river pollution and disturbance. Disturbance is something that has been increasing for the past quarter of a Century. But recent years have seen an upsurge in such activities as pleasure boating and freshwater angling, to a point where previously inaccessible backwaters are now receiving the attention of public pressure. T h e present practise of Clearing away all bankside Vegetation, in an effort to improve the river's flow, is a serious encroachment on surviving otter habitat. Excessive disturbance has serious repercussions for the otter. If a river contains several stretches of disturbed habitat it has the effect of fragmenting the otter territories and irtipeding the movement of individuals along the river. Otters are very reluctant to pass through long stretches of river devoid of Vegetation cover, and their tolerance of areas subject to intensive human pressure is very small. If this Situation persists on a river, otter territories become contracted, and casualties cannot be replaced in the normal way, ultimately the river loses its otters. It is probably this process that is responsible for the loss of otters on rivers like the Gipping and the Lark. Today it can be seen in progress on rivers such as the Waveney and the Stour. One of the projected aims of this survey was, if it proved feasible, to put forward suggestions for conservation measures.